I try this engine today and got 7500 rpm on prop 13x6 MS at the best
Do you know if this the best rpm I can get ??

A Graupner 12x6 should get you close to 10,000

A 12-7 apc will give you about 9000 rpm's when set right

Hi
I try 12x6 K series and get 8500 only why ???

Make sure you are not overcompressed 1/2 turn will cost you at least 500rpm slack off the compression screw till you get a miss then slowly turn in till goes away also you should be at top rpm at about 80% open too much (100% and it may slow down)
then tweek the needle
it may have to go a little richer or leaner bigger prop more load less compression needed smaller prop more compression needed
you have to tune to the prop load nad of course make sure your fuel has not suffered an ether loss it will require more compression run hot and of course rpm loss if ether% has dropped
also the K series prop is a wide blade used a lot on 4 strks so at 8500 you may have a lot of thrust so you have a combination of things here reducing your rpm that prop should pull like mad at 8500
also APC props turn quicker 11x7 or 12x6 may give you more in the rpm

Just a point of info I ran my ST40 davis head today 14x4 wood zinger 8200 and a 12x4 wood zinger 9900 both have wide blades
compared to other props and lots of thrust

I try to adjust the compression as explained here and by Mr. Cultton but
I open the compression screw to the end and I do not get any misfire.
Last time I work with compression screw open to the end and I feel that the compression still too high.
The diesel head is Davis head.

What I made wrong ??

I had a problem with one of my ST G20-15 diesels. I could not decompress it enough because the contrapison was hitting the head. I put in a head gasket between the cylinder and head and that was just enough clearance. It sounds like you are running overcompressed. Are you getting black exhaust?

Jim

It could be the prop, that is a wide bladed fourstroke prop, it doesn't look like it would be easy to turn. Mine turns a ProZinger 12x7 at 9,000 on Davis Oily Mix fuel.

Add an other head gasket that should allow you some leeway I have (3) on my tt61 pro took that many so I could adjust the head
screw out enough to get a miss

Barkai,


I will be converting an MVVS .49 to Diesel in a couple of weeks.

I think you may want to bring a few prop sizes over and see what it can do.

Keep in touch.